Re: [for-next PATCH v2 1/2] RDMA/rxe: Remove unnecessary mr testing

[Li Zhijian]

On 24/10/2022 10:25, Zhu Yanjun wrote:
> > > > > +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
> > > > > @@ -778,6 +778,7 @@ static enum resp_states read_reply(struct rxe_qp *qp,
> > > > >           if (res->state == rdatm_res_state_new) {
> > > > >                   if (!res->replay) {
> > > > >                           mr = qp->resp.mr;
> > > > > +                       WARN_ON(!mr);
> > > > >                           qp->resp.mr = NULL;
> > > > >                   } else {
> > > > >                           mr = rxe_recheck_mr(qp, res->read.rkey);
> > > > > @@ -811,8 +812,7 @@ static enum resp_states read_reply(struct rxe_qp *qp,
> > > > >
> > > > >           rxe_mr_copy(mr, res->read.va, payload_addr(&ack_pkt),
> > > > >                       payload, RXE_FROM_MR_OBJ);
> > > > > -       if (mr)
> > > > > -               rxe_put(mr);
> > > > > +       rxe_put(mr);
> > > > >
> > > > >           if (bth_pad(&ack_pkt)) {
> > > > >                   u8 *pad = payload_addr(&ack_pkt) + payload
> > > > > --
> > > > > 2.31.1
> > Li is correct that the only way mr could be NULL is if qp->resp.mr == NULL. So the
> What I am concerned about is if "WARN_ON(!mr);" should be added or not.
> IMO, if the root cause remains unclear, this should be a problem.
> Currently this problem is not fixed. It is useless to send a debug
> statement to the maillist.

As per Bob's explanation,  no 'WARN_ON(!mr)' is needed.
I will update the patch soon.

> Zhu Yanjun
>
> > 'if (mr)' is not needed if that is the case. The read_reply subroutine is reached
> > from a new rdma read operation after going through check_rkey or from a previous
> > rdma read operations from get_req if qp->resp.res != NULL or from a duplicate request
> > where the previous responder resource is found. In all these cases the mr is set.
> > Initially in check_rkey where if it can't find the mr it causes an RKEY_VIOLATION.
> > Thereafter the rkey is stored in the responder resources and looked up for each
> > packet to get an mr or cause an RKEY_VIOLATION. So the mr can't be NULL. I think
> > you can leave out the WARN and just drop the if (mr).
Very thanks for your explanation

Thanks
Zhijian

> > Bob